A decoloring apparatus configured to decolor a colorant from a sheet on which an image is formed using a decolorable colorant and in which the number of sheets on which the colorant is decolored is counted, and the amount of a reduction in environmental burdens is displayed based on the number of the sheets on which the colorant is decolored is known in the related art. In addition, a decoloring apparatus including a card reader, in which the card reader stores the number of colorant-decolored sheets for each user authenticated by an ID card, and an environmental load contribution ratio is displayed for each user is known. An environmental contribution supporting apparatus is also known in which the number of saved sheets of a group to which a user belongs is calculated from the number of reduced sheets for the group to give a score regarding a reduction in environmental burdens.
In the image erasing apparatus in which the number of colorant-decolored sheets is controlled for each user or group, a method of counting up, whenever an image is erased, an erasing counter based on user information or group information which is authenticated during use of the image erasing apparatus is generally used.
However, in such image erasing apparatus, it is impossible to determine whether or not an authenticated operator is the owner of an image. In the image erasing apparatus, when an image is erased, it is impossible to determine whether or not the erased image belongs to a user or group (hereinafter, also referred to as “owner”) that prints the image. Therefore, there is a problem in that, for example, even if another owner erases an image on a sheet, an erasing counter of the authenticated user or group is counted up. If a sheet on which an image of another owner is formed or a sheet of another owner which is mixed with sheets of the owner passes through the image erasing apparatus, the image on the sheet may be erased.